Incremental gear drive

ABSTRACT

An incremental gear drive comprises input and output shafts journalled for rotation about a common axis, the shafts being drivingly connected through a multiple reduction gear train in a rotatable housing, the gears of which are caused to rotate at a controlled speed either the same as the housing or different therefrom to effect a controlled difference of speed between the input and output shafts. The unit includes a control shaft which is driven by a control motor, connected to the first pinion of the gear train.

United States Patent 91 East et al.

[ 1 Jan.23, 1973 [54] INCREMENTAL GEAR DRIVE [75] Inventors: FrankGeorge East; Frank Rouget Bichard, both of Toronto, Ontario, Canada [73]Assignee: Combined Engineered Products Limited, Toronto, Ontario, Canada[22] Filed: Dec. 28, 1970 [21] Appl. No.: 97,414

[30] Foreign Application Priority Data Jan. 7, 1970 Great Britain..717/70 [52] 11.8. C1. ..74/687, 74/675, 74/681 [51] Int. Cl. ..F16h47/04, Fl 6h 37/08 [58] Field of Search ..74/675, 687, 681, 689

[56] References Cited UNITED STATES PATENTS 1/1970 Giles ..74/68710/1959 Parkeret a1. ..74/675 1,621,915 3/1927 Weston ....74/675 X2,675,716 4/1954 Harlow et a1 ..'.....74/675 2,772,580 12/1956 Miura eta1 ....74/675 3,298,250 1/1967 Moss et al. ...74/675 3,405,573 10/1968Takekawa ....74/687 3,424,030 1/1969 Mennit ..74/675 PrimaryExaminer-Milton Kaufman Assistant Examiner-Thomas C. PerryAttorney--Meybee & Legris [57] ABSTRACT An incremental gear drivecomprises input and output shafts journalled for rotation about a commonaxis, the shafts being drivingly connected through a multi ple reductiongear train in a rotatable housing, the gears of which are caused torotate at a controlled speed either the same as the housing or differenttherefrom to effect a controlled difference of speed between the inputand output shafts. The unit includes a control shaft which is driven bya control motor, connected to the first pinion of the gear train.

7' Claim '8; s 515mg Figures PATENTEDJANZSIHH 3.712.153

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FIG 'I FRANK GEORGE EAST v FRANK ROUGET BICHARD AT TOR NEYS PATENTEDJAI23 I975 3.712.153

sum 3 0F 3 INVENT S. NK GEORGE ST NK ROUGET BICHARD ATTORNEYSINCREMENTAL GEAR DRIVE This invention relates to incremental gear drivesthat is to say gear transmission which permit two shafts to be drivenfrom a common power source with a controlled variable difference inspeed between the shafts. Incremental gear drives are commonly used instretch flattening mills and similar applications.

After metal strip has been rolled to a required thickness it requiresflattening. Out-of-flatness may consist of waviness at the edges orbulging in the middle of the strip. This latter condition is commonlyknown in the trade as oil canning.

One of the most successful methods of correcting the out-of-flatness orrolled metal strip is by continuously stretching the strip by an amountwhich subjects the material of the strip to a stress somewhat more thanthe elastic limit or yield point but below a stress that would exceedthe ultimate strength of the material and cause rupture of the strip. Inthis method the strip is unwound from a pay-off reel by passing itaround a series of positively driven rolls, and is caused to stretch bypassing it over another series of positively driven rolls running at acontrolled higher speed, whereby the strip is stretched and then rewoundon a take-up reel. Tension is applied at the payoff and take-up reels tocreate enough friction between the rolls and the strip to preventslippage.

With this flattening method the power input from the drive motor needonly be sufficient to overcome friction and to supply the powerequivalent of the strip tension at the speed difference between thepay-off and take-up reels. However any unit which transmits this tensionat the strip speed (rather than merely at said speed difference) must bedesigned to handle a high horsepower, normally 8 to times the powerinput from the driving motor.

Conventional gear drives used in the above flattening method consist ofa differential unit having bevel gears in a carrier, incremental speedsbeing obtained by rotating the carrier. Such a unit must be quite large,

and the gear tooth velocity (the velocity at the mesh of the future therequisite velocity may be beyond the,

capabilities of available spiral bevel gears.

The present invention provides a device whereby difference in speedsbetween two shafts can be accomplished by driving the shafts from acommon drive motor, one of the shafts being driven through a train ofgears which are so arranged that at a base or synchronous speed, atwhich the shafts rotate at the same speed, the gears of the train do notrotate around their respective axes. The gears rotate around their axesonly to provide a difference in speed between the shafts. The gear toothvelocity being dependent upon only the speed differential required,rather than upon the base or synchronous speed, the resulting maximumgear tooth velocitycan be of the order of only l0 percent of the geartooth velocity in the conventional arrangement mentioned above.

Accordingly, the present invention provides an in- 'cremental gear drivecomprising an input shaft, an outa common axis, a central gear-rigidlyconnected to one of the shafts for rotation therewith, a rotatablehousing rigidly connected to the other of said shafts for rotationtherewith, multiple countershaft gears journalled in the rotatablehousing and meshing with the central gear, and variable speed drivemeans drivingly connected with the multiple countershaft gears wherebyto provide a controlled variable difference of speed between the inputand output shafts. Preferably one of the shafts is hollow and the otherextends into the hollow shaft so that the power output can be taken fromthe same end of the incremental drive unit as the power input to it, thecontrol motor being located at the opposite end and the rotatablehousing being coaxial with the shafts between said ends.

Preferred embodiments of the invention are illustrated by way of examplein the accompanying drawings, in which:

FIG. 1 is a diagrammatic plan view of a stretch flattening mill driveincorporating the incremental gear drive of the invention;

FIG. 2 shows a longitudinal vertical section taken through the axis ofthe incremental gear drive;

FIG. 3 is a section on line 3-3 in FIG. 2;

FIG. 4 shows in section a detail of a modification of the incrementalgear drive; and

FIG. 5 shows in section a detail of another modification of theincremental gear drive.

Referring to FIG. 1, a metal strip stretch flattenin mill has a firstset of rolls coupled to shaft extensions 1 and a second set of rollscoupled to shaft extensions 2, which are driven at controllablydifferent speeds from a common drive motor 3 through respectivereduction gear trains 4,5. The motor 3 has a variable speed output shaftso the basic speed of the strip to be flattened can be varied. Thedifference of speeds between the two sets of rolls is controlled bymeans of an incremental gear unit 6. The incremental gear unit 6 has aninput shaft which is driven from the drive motor 3 through a gear train7, and an output shaft which is connected to the reduction gear train 5and driven at a speed which differs from the speed of the input shaft inaccordance with the speed of a control motor 8. The control motor 8 maybe a hydraulic motor supplied by a hydraulic pump 9, the output of whichis made dependent upon the speed of the drive motor 3 as hereinafterdescribed. A web of metal strip travelling between the rolls connectedto shaft extensions I and 2 is stretched to a degree dependent upon thedifference in speed between the rolls driven by shafts 1 and 2. Thestrip must travel in the direction from the rolls rotating at the lowerspeed to the rolls rotating at the higher speed.

The incremental gear unit 6 is illustrated in greater detail in FIGS. 2and 3. The unit comprises a stationary housing or frame 10 having a pairof opposite end faces 10a, 10b, the housing or frame being rigidlymounted on a base 11. An input shaft 12 and an output shaft 13 arejournalled in the housing 10 for rotation about a common axis, the inputshaft 12 being supported in a bearing- 14 and the output shaft 13 beingsupported in bearings 15 and 15a. The input shaft 12 is constructed as ahollow sleeve along which the output shaft extends axially, the twoshafts extending from the one end face 10a of the housing 10. The inputand output shafts are connected to respective shaft'extensions 12a, 13aby means of shaft couplings 12b, 13b.

Also journalled in the housing and extending from the end face 10bthereof is a control shaft 16, the control shaft 16 being coaxial withthe shafts 12 and 13 and supported by a bearing 17. A hollowintermediate shaft 18, into which the output shaft 13 extends, issupported at one end by a bearing 19, this shaft being coaxial with theother three shafts and journalled for rotation about said common axis.The inner end of the input shaft 12 is constructed as a flange 20, towhich one end of a rotatable housing assembly 21 is rigidly bolted bybolts 22, the other end of the rotatable housing assembly beingsupported by a bearing 23 mounted in the end face 10b of the stationaryhousing. The rotatable housing assembly 21 carries a first set ofcountershafts 24, and a second set of countershafts 25, there beingthree countershafts in each set which are equally spaced around saidcommon axis. As illustrated in FIG. 2, the countershafts 24 arejournalled in bearings 26a, 26b, and the countershafts 25 are journalledin bearings 27a, 27b.

The rotatable housing assembly is not normally immersed in oil, oilpassages 41 being provided for leading oil from an outside source to thevarious bearings and gear meshes.

Keyed or otherwise rigidly connected to the output shaft 13 for rotationtherewith is acentral gear, or first externally toothed sun gear 28,which meshes with a first set of countershaftgears or pinions 29 thatare rotatable with the countershafts 24.

Clearly, as the motor driven input shaft 12 is rotated, power will betransmitted to the output shaft 13 through the rotatable housing 21,gears 29, and central gear 28. Any difference of speed between the inputand output shafts is determined by the speed of rotation of the gears29, which speed is variably controlled from the control motor 8 throughreduction gearing that will now be described.

Rotatable with each of the countershaft gears 29 and carried by thecountershaft 24 is a countershaft third gear 30, this second set ofthree countershaft gears 30 meshing with a second externally toothed sungear 31 on the intermediate shaft 18. The intermediate shaft, which issupported at one end by the bearing 19, is thus also supported at itsother end by engagement with the gears 30. A third externally toothedsun gear 32, rotatable with the sun gear 31, is keyed or otherwiserigidly connected to the intermediate shaft, and this meshes with athird set of three pinions, or countershaft gears 33 carried by thecountershafts 25. A fourth set of countershaft gears 34 carried by thecountershafts 25 are rotatable with the corresponding gears 33, each ofthe countershaft gears 34 meshes with a pinion, or fourth externallytoothed sun gear 35, which is rotatable with the control shaft 16.

The control motor 8, which is shown as a hydraulic motor 8 having fluidconnections 36, is bolted by bolts 37 to the end face 10b of thestationary housing. This control motor has an output shaft 38 connectedby a coupling 39 to the control shaft 16.

When the control shaft 16 is rotated at the same speed as the inputshaft 12, and hence at the speed of the rotary housing assembly 21,there can be no rotation of the planet gears 29 about their individualaxes, since there is no relative rotation between the control shaft andthe rotatable housing assembly. The central gear 28 is therefore lockedto the rotating housing assembly and so the speed of the output shaft 13will be the same as the speed of the input shaft 12. However, when thecontrol shaft 16 is rotated by the control motor at a speed which isdifferent from the speed of the input shaft, the consequent rotation ofthe reduction gearing within the rotatable housing assembly will causethe gears 29 to rotate at a speed determined by the difference speed,and hence will cause the output shaft speed to be greater or less thanthe input shaft speed, the difference in speed being determined, ofcourse, by the speed of the control shaft.

FIG. 4 shows a detail of a modification of the unit described above. Inthis figure the same reference numerals are used to denote elementscorresponding to elements shown in FIG. 2. The modified unit differsfrom the unit of FIG. 2 in this respect, that the motor 8 is bolted to aflange 42 on the rotatable housing 21, so that it rotates bodily withthe rotatable housing at the speed of the input shaft. Therefore, whenthe control motor 8 is not energized there will be no relative rotationbetween the control shaft 16 and the rotatable housing assembly 21, andso the gears 29 will not rotate about their own axes, the output shaft13 will therefore be locked to the input shaft. When the control motor 8is energized so that its output shaft rotates relative to the motorcasing, a difference speed is transmitted to the gears 29 and so theoutput shaft will rotate faster or slower than the input shaft by anamount determined by such difference speed.

FIG. 5 shows a detail of another modification, which corresponds moreclosely to the diagrammatic representation in FIG. 1. In thismodification, the stationary housing 10 is formed with an extension 50in which an auxiliary shaft 43 is journalled. The auxiliary shaft 43 issupported by bearings 44a, 44b and extends parallel to the input shaftsaxis, which is of course also the axis of the control shaft 16. Theauxiliary output shaft extends from an extension of the end face 10b ofthe stationary housing. A tubular, sleeve 45 extending from therotatable housing assembly (not shown) and rotatable therewith, supportsthe control shaft 16 coaxially by a bearing 46.

Keyed to the outer surface of the tubular sleeve 45 is a gear 47 whichmeshes with a gear 48 on a countershaft 49, the gear 48 in turn meshingwith a gear 51 on the auxiliary shaft 43. In this way the auxiliaryoutput shaft is rotated at the speed of the rotatable housing assembly,and hence at the speed of the input shaft. This is a particularlyadvantageous arrangement where it is necessary to maintain a constantspeed ratio of the input and output shafts, rather than an absolutespeed difference, for it becomes possible to energize the control motor8 from a power unit driven from the shaft 43 at the input shaft speed,the power unit being conveniently mounted beside the control motor. Inthe illustrated example the control motor 8 is a hydraulic motorsupplied from a hydraulic pump 9 mounted on the end face 10b. Thehydraulic pump 9 is driven from the auxiliary shaft 43, its outputvolume being determined by the input shaft speed and the speed of thecontrol motor being determined by this output volume.

lt is to be understood that although the control motor 8 has beendescribed throughout as a hydraulic motor, it may alternatively be avariable speed electric motor or other prime mover. Whether the motor 8be an electric motor, a hydraulic motor or other prime mover, it may bemounted on an end face of the stationary casing as shown in FIGS. 2 andS, or it may be mounted so as to rotate with the rotary housing assemblyas shown in FIG. 4; in the latter case it is of course necessary tosupply power to the motor through a rotary joint (in the case of ahydraulic motor) or through slip rings (in the case of an electricmotor.)

WHAT WE CLAIM AS OUR INVENTION IS:

1. An incremental gear drive comprising:

an input shaft and an output shaft, said shafts being journalled forrotation about a common axis,

a first externally toothed gear rigidly connected to one of said shaftsfor rotation therewith,

a rotatable housing rigidly connected to the other one of said shaftsfor rotation therewith,

an intermediate shaft journalled for rotation about said common axis,

a control shaft,

a first double speed reduction gear train for transmitting torque fromthe intermediate shaft to said one shaft, said first double speedreduction gear train comprising:

a. a first set of countershaft gears journalled in said housing andmeshing with the first externally toothed gear,

b. a second externally toothed gear rigidly connected to theintermediate shaft for rotation therewith, and

c. a second set of countershaft gears rotatable with the first set ofcountershaft gears and meshing with said second externally toothed gear;

a second double speed reduction gear train for transmitting torque fromthe control shaft to the intermediate shaft, said second double speedreduction gear train comprising:

a. a third externally toothed gear rigidly connected to the intermediateshaft for rotation therewith,

b. a fourth externally toothed gear rigidly connected to the controlshaft for rotation therewith,

c. a third set of countershaft gears journalled in the housing andmeshing with the third externally toothed gear, and

d. a fourth set of countershaft gears rotatable with the third set ofcountershaft gears and meshing with the fourth externally toothed gear;

and variable speed drive means connected to the control shaft whereby toproduce a controlled variable difference of speed between said input andoutput shafts.

2. An incremental gear drive according to claim 1, wherein the controlshaft is journalled for rotation about said common axis.

3. An incremental gear drive according to claim 2 wherein one of saidinput and output shafts is a hollow sleeve, the other of said input andoutput shafts extending along the hollow sleeve.

4. An incremental gear drive according to claim 3, wherein the variablespeed drive means comprises a motor having a casing which is rigidlyconnected to the input shaft for rotation therewith.

5. An incremental gear drive according to claim 3, wherein the variablespeed drive means is a hydraulic motor.

6. An incremental gear drive according to claim 5,

including an auxiliary shaft journalled for rotation about an axis whichis parallel to and spaced from said common axis, a gear trainoperatively connecting the auxiliary shaft with said input shaft, and ahydraulic pump for supplying the motor, the hydraulic pump being drivenfrom said auxiliary shaft.

7. An incremental gear drive according to claim 6, further comprising astationary housing wherein said input and output shafts, and saidintermediate, control and auxiliary shafts are journalled, the input andoutput shafts extending from one end of the stationary housing, theauxiliary shaft and the control shaft extending from the other end ofthe stationary housing, and the hydraulic pump and motor being mountedon said other end of the stationary housing and operatively connected tosaid auxiliary shaft and control shaft respectively.-

1. An incremental gear drive comprising: an input shaft and an outputshaft, said shafts being journalled for rotation about a common axis, afirst externally toothed gear rigidly connected to one of said shaftsfor rotation therewith, a rotatable housing rigidly connected to theother one of said shafts for rotation therewith, an intermediate shaftjournalled for rotation about said common axis, a control shaft, a firstdouble speed reduction gear train for transmitting torQue from theintermediate shaft to said one shaft, said first double speed reductiongear train comprising: a. a first set of countershaft gears journalledin said housing and meshing with the first externally toothed gear, b. asecond externally toothed gear rigidly connected to the intermediateshaft for rotation therewith, and c. a second set of countershaft gearsrotatable with the first set of countershaft gears and meshing with saidsecond externally toothed gear; a second double speed reduction geartrain for transmitting torque from the control shaft to the intermediateshaft, said second double speed reduction gear train comprising: a. athird externally toothed gear rigidly connected to the intermediateshaft for rotation therewith, b. a fourth externally toothed gearrigidly connected to the control shaft for rotation therewith, c. athird set of countershaft gears journalled in the housing and meshingwith the third externally toothed gear, and d. a fourth set ofcountershaft gears rotatable with the third set of countershaft gearsand meshing with the fourth externally toothed gear; and variable speeddrive means connected to the control shaft whereby to produce acontrolled variable difference of speed between said input and outputshafts.
 2. An incremental gear drive according to claim 1, wherein thecontrol shaft is journalled for rotation about said common axis.
 3. Anincremental gear drive according to claim 2 wherein one of said inputand output shafts is a hollow sleeve, the other of said input and outputshafts extending along the hollow sleeve.
 4. An incremental gear driveaccording to claim 3, wherein the variable speed drive means comprises amotor having a casing which is rigidly connected to the input shaft forrotation therewith.
 5. An incremental gear drive according to claim 3,wherein the variable speed drive means is a hydraulic motor.
 6. Anincremental gear drive according to claim 5, including an auxiliaryshaft journalled for rotation about an axis which is parallel to andspaced from said common axis, a gear train operatively connecting theauxiliary shaft with said input shaft, and a hydraulic pump forsupplying the motor, the hydraulic pump being driven from said auxiliaryshaft.
 7. An incremental gear drive according to claim 6, furthercomprising a stationary housing wherein said input and output shafts,and said intermediate, control and auxiliary shafts are journalled, theinput and output shafts extending from one end of the stationaryhousing, the auxiliary shaft and the control shaft extending from theother end of the stationary housing, and the hydraulic pump and motorbeing mounted on said other end of the stationary housing andoperatively connected to said auxiliary shaft and control shaftrespectively.